Control method for gas burners

ABSTRACT

The invention relates to a control method for gas burners for providing a gas-air mixture.  
     According to the invention, the ionization signal is only used for setting the mixing ratio dependent on the gas quality when the burner flame completely sweeps over the sensor generating the ionization signal. Outside the above-mentioned range, i.e. when the burner flame does not completely sweep over the sensor generating the ionization signal, the gas-air mixture is controlled dependent on the previously determined mixing ratio.

[0001] The invention relates to a control method for gas burners according to the preamble of claim 1.

[0002] Control methods for gas burners are used for providing a gas-air mixture, i.e. for supplying a gas flow and a combustion air flow to a burner.

[0003] In order to ensure an optimum and complete combustion of the fuel, i.e. the gas, within the gas burner, the latter has to be provided with an appropriately balanced gas -air mixture. The ratio between the gas flow and the combustion air flow, and between the gas pressure and the combustion air pressure, respectively, is referred to as mixing ratio or composition ratio.

[0004] However, since the quality of the gas provided by the gas supply varies—the quality of gas is defined by a so-called Wobbe index—, the gas-air mixture has to be appropriately varied dependent on the quality of the gas to ensure an optimum and complete combustion.

[0005] For making it possible to consider the quality of the provided gas, the prior art discloses control methods according to which an ionization signal of a sensor, in particular of a measuring electrode projecting into the burner flame of the gas burner, is used for adapting the gas-air mixture to different gas qualities. In this respect, it can be referred to the DE-A-44 33 425, DE 39 37 290 A1, as well as to the DE 195 39 568 C1.

[0006] In the known control methods for gas burners according to which an ionization signal is used, this ionization signal is used over the whole operating range of the burner for adapting the gas-air mixture to different gas qualities. However, when the operating loads of the burner are low, the ionization signal strongly depends on external influences and consequently does not provide any reliable information on the combustion conditions actually prevailing in the burner. Accordingly, the control methods according to the prior art lead to an instable and, thus, insufficient control.

[0007] Starting out from this, the present invention is based on the problem of providing an improved control method for gas burners. According to the invention, the problem is solved by a control method comprising the features of claim 1.

[0008] Preferred further developments of the invention result from the subclaims and the description.

[0009] The control method for gas burners is used for providing a gas-air mixture for a burner. For this purpose, a gas flow and a combustion air flow are supplied to the burner. The ratio between gas flow and combustion air flow, and the ratio between gas pressure and combustion air pressure, respectively, is referred to as mixing ratio.

[0010] The combustion process in the burner is monitored by means of a sensor generating an ionization signal. Information on the combustion process and, thus, on the existing gas quality can be obtained from the ionization signal.

[0011] According to the invention, the ionization signal is used for setting the mixing ratio dependent on the gas quality exclusively when the burner flame completely sweeps over the sensor generating the ionization signal. The underlying idea of this feature according to the invention is that the ionization signal provides a reliable information on the combustion process only during this working or operating state of the burner.

[0012] Outside the above-mentioned range, i.e. when the burner flame does not completely sweep over the sensor generating the ionization signal, the gas-air mixture is controlled dependent on the previously determined mixing ratio.

[0013] The condition whether or not the burner flame completely sweeps over the sensor generating the ionization signal can, for example, be verified by an additional optical flame monitoring means. 

1. A control method for gas burners for providing a gas-air mixture, namely for supplying a gas flow and a combustion air flow to a burner, with an ionization signal of a sensor being used for adapting the gas -air mixture to different gas qualities, characterized in that a) the ionization signal is only used for setting a mixing ratio when the burner flame completely sweeps over the sensor generating the ionization signal, b) outside this range, i.e. when the burner flame does not completely sweep over the sensor generating the ionization signal, the gas-air mixture is controlled dependent on this mixing ratio. 